The present invention relates to an attachment for use with a two-wheeled vehicle, and to a wheel for a two-wheeled vehicle having such attachments. In particular is the invention related to a bicycle which may be assisted by an electric or another motor. Drive or assistance through other motors is possible as well.
Present-day two-wheeled vehicles in general and bicycles in particular both for recreational and professional uses are expected to satisfy elevated requirement levels. A fundamental aspect is concerned with the most efficient propulsion of a bicycle possible. This is the case in particular on a professional scale since minute advantages may already significantly affect the results of competitions.
For example the weight of the bicycle with all of the attachments, a low rolling resistance, and in particular aerodynamics play the largest role. Specifically in racing even minimal savings in weight or improvements of aerodynamics may lead to significant competitive advantages. These areas are directly interrelated so as to be of specific interest regarding further developments in these fields.
Furthermore, advantages in aerodynamics are currently a major issue among other things in bicycles having an auxiliary motor. These motor-assisted, two-wheeled vehicles are gaining popularity not only with the elderly but in particular with long-distance riders and for use in mountainous regions. Commuting workers also increasingly use these bicycles. In this conjunction enhanced aerodynamics will increase the operational range of two-wheeled vehicles and thus the service life of the battery.
Air turbulences in all kinds of different places play a role in aerodynamics. Bicycle racers use for example special tight-fitting clothes and they assume an aerodynamic riding position on the bicycle, employing special handlebars. In this way they decrease drag to achieve better performance.
Air turbulences at the bicycle itself should also be avoided as much as possible or minimized. One of the problems is associated with the wheels.
A classical bicycle wheel consists of a central hub having mounting points for spokes formed on both sides thereof. The spokes are hooked into holes in these mounting points and fastened on the other side to so-called spoke nipples guided through or into the rim. The spoke side facing the spoke nipple has a thread which is screwed into an internal thread of the spoke nipple. This system allows to vary the spoke tension and thus adjust the wheel optimally.
For adjusting the spoke tension a range of variants has become known. For example it is possible to have the spoke nipple, which is up to 10 or 20 mm in length and approximately 3 mm to 8 mm in diameter, slightly protrude radially inwardly from the rim. The protruding portion has a number of flat faces. This allows great ease of externally adjusting the spoke tension using a dedicated tool. The drawback of this is, however, that the protruding portions of the spoke nipples cause undesirable aerodynamic effects since air turbulences occur at the flat spoke nipple faces. The exposed spoke nipple portions at the top of the wheel will move at approximately double the bicycle speed so as to effectively quadruple the drag, which is a drawback.
From EP 0 808 728 B1, a device having a pair of cover rings has become known. The two specifically configured cover rings cover the entire inner radius of the rim and the spoke nipples of the conventional spoke wheel at their centers. This type of cover involves the drawback, however, that the large shaped parts considerably increase the total weight of the wheel and that they are not suitable for all the rims since they must be specifically manufactured to a given inner rim radius and to the corresponding spoke distances. This does not only make the solution heavy in weight but expensive as well.
Another option for mounting the spokes to the spoke nipples is known specifically for present-day wheels of fiber-reinforced plastic. Again in this case the extremely thin spokes are screwed into spoke nipples and tensioned or released by way of rotating the spoke nipple. However, the spoke nipples in this variant tend to lie entirely inside the hollow rim. An advantage thereof are considerably improved aerodynamics since no undesirable air turbulences can occur at the spoke nipples.
A particular drawback of this type of fastening is the particularly intricate tensioning of the wheel. For readjusting the spoke tension it may be necessary to remove from the rim the jacket, the tube, and the rim tape so as to modify the spoke tension from the inside for example by means of a screwdriver. When wheel adjustment is finished, all the parts must be reassembled. This is complicated and requires much time. Adhesive-bonded tube tires require still more efforts.
DE 8 912 607 describes aerodynamic spoke covers intended to reduce the spoke drag in the radially outwardly region. To this end, streamlined elements are placed onto the spokes. The drawback of this cover type is the large size which has a negative influence on the total weight. These covers are furthermore highly susceptible to side-wind effects and may twist in side winds. A simpler and more reliable method is to use blade spokes.
Furthermore, aerodynamic wheels of fibrous composite materials have become known which are manufactured integrally for example as three-spoke wheels. The drawback of this construction type is, however, that manufacturing these wheels involves manual labor which makes them very expensive. Moreover, three-spoke wheels are highly susceptible to side-winds and due to the integral manufacturing the spoke tension cannot be readjusted.